WASHINGTON — Mexico is standing firm against President Donald Trump's plan to impose auto import tariffs, with its ambassador to the U.S. saying it's "hard to make the argument that there's a national security issue" in goods traveling from his country to its northern neighbor.

Gerónimo Gutiérrez on Thursday joined a cavalcade of car manufacturers, auto dealers and diplomats in relaying concerns to the U.S. Commerce Department over the proposed levies.

"That certainly would be a big blow," he said this week at a forum hosted by Politico Pro, ahead of the hearing to investigate if the U.S. should proceed with the auto tariffs. "It would have huge consequences worldwide."

AMLO, as the president-elect is known, had stirred fears that his Mexico-first approach might topple trade norms that are vital to economies on both sides of the border, particularly in Texas.

But the incoming administration has pledged strong coordination on trade with the country's existing leadership, including Gutiérrez, particularly when it comes to highlighting the importance of the North American Free Trade Agreement that binds Mexico, the U.S. and Canada.

Time will be the true test. Still, the early signs on trade cannot be ignored.

"What we're all seeing here is the extraordinary sense of continuity between the incoming and outgoing administrations," said Duncan Wood, director of the Mexico Institute at the Washington-based Woodrow Wilson International Center for Scholars.

Mexico trade important to Texas

The two economies have forged strong bonds over the nearly 25 years since NAFTA took hold. Mexico is Texas' largest trading partner, covering nearly $190 billion in trade. About 1 million Texas jobs are supported by trade with Mexico and Canada, according to the U.S. Chamber of Commerce.

"It has played a significant role in the diversification of Texas' economy and fostered a robust, yet stable labor marker," Texas Gov. Greg Abbott wrote earlier this year, referring to NAFTA.

But Trump has not avoided tangling with Mexico and its current president, Enrique Peña Nieto. That tension has often centered on immigration, including Trump's promise to build a "big, beautiful" border wall and force Mexico to somehow pay for it.

Trade also has been at the forefront.

Trump has threatened to withdraw from NAFTA, calling it the "worst trade deal ever." He enacted tariffs on steel and aluminum imports, causing Mexico and other countries to retaliate. Now he's considering levies on imports of automobiles and automotive parts from across the globe.

"What sort of signals is the United States sending to Mexico?" said Eric Farnsworth, vice president of the Council of the Americas. "That's a more challenging issue."

Focus on auto tariffs

The Trump administration's investigation into auto tariffs focuses on national security concerns. The president himself often presses the issue as a matter of fairness.

He rages that the European Union, for instance, has a 10 percent duty on automobiles from the U.S. that's higher than the U.S.'s 2.5 percent barrier on cars going the other way. (Left unsaid is that the U.S. famously has a 25 percent levy on imported light trucks and commercial vans.)

"If we don't negotiate something fair, then we have tremendous retribution, which we don't want to use," Trump said on Wednesday.

The auto industry, both domestic and foreign, is leading the revolt. Jennifer Thomas of the Alliance of Automobile Manufacturers summed it up by telling the Commerce Department on Thursday that "higher tariffs will harm American workers, families and the economy."

Most individual automakers didn't testify at the hearing. But they've hardly remained silent.

Groups representing car dealerships, auto parts manufacturers and service shops also sounded off on the levies at the daylong hearing on Thursday. Even the United Automobile Workers union, while urging action, cautioned against a rash approach that produces "unforeseen consequences."

Diplomatic officials from key U.S. allies rounded out that pushback, with Gutiérrez pointing specifically to NAFTA — and the trade produced by it — as a strength for the U.S. auto industry.

The Mexican ambassador to the U.S. said it's "no secret that the supply chains that have been built over the last 25 years between the three NAFTA partners" are a key factor in competitiveness, though critics point out that low-wage jobs in Mexico are part of that equation.

Consider auto parts, which often cross borders between the NAFTA nations multiple times in the manufacturing process for a car. Indeed, the U.S. and Mexico are both the top auto parts supplier to each other's automotive industry, the Mexican government said.

The end result is that even vehicles produced in Mexico and imported to the U.S. typically have significant amounts of U.S.-made content within them.

"A strong and successful United States is in the interest of Mexico as much as a strong and successful Mexico is in the interest of the United States," Gutiérrez said.

Geronimo Gutierrez, Mexico's ambassador to the United States, says it would be a "big blow" if the U.S. imposes tariffs on imports of automobiles and automobile parts.

(Irwin Thompson/Staff Photographer)

President Donald Trump has pointed to potential auto tariffs as a negotiating tool. "If we don't negotiate something fair, then we have tremendous retribution, which we don't want to use," he said this week.

(Jabin Botsford/The Washington Post)

Mexico's President-elect Andres Manuel Lopez Obrador's Mexico-first rhetoric stirred fears about the fate of NAFTA. But he's taken a more conventional stance in favor of the deal of late.

(Pedro Pardo/Agence France-Presse)

Commerce Secretary Wilbur Ross on Thursday said it's "too early" to say if the U.S. will ultimately enact tariffs on auto imports. But he stressed that the U.S. auto industry is "indispensable."

(Manuel Balce Ceneta/The Associated Press)

Mexican President-elect Andres Manuel Lopez Obrador's appointed economy minister, Graciela Marquez, has tamped down earlier worries about AMLO's trade approach. "Mexico would not close itself off because Mexico needs to grow," she said in May.

(Pedro Pardo/Agence France-Presse)

New auto tariffs would disrupt that dynamic, producing ripple effects through the economy in the U.S., Mexico and beyond. It would also be a nonstarter for Mexico, posing severe complications, at the very least, in ongoing NAFTA negotiations.

Gutiérrez this week said he wouldn't speculate on how Mexico would respond if the U.S. moves ahead. But Mexico has set somewhat of a precedent by retaliating against Trump's metal tariffs.

"We get no pleasure from doing that. We were, in a sense, forced into it," he said at the Politico Pro event. "If you are the middle of a negotiation ... and you have something like that established, the only way you can continue to be at the table is if you do that."

The ambassador projected hope that a successful resolution on NAFTA would render the issue over auto tariffs null.

That's part practical, with Gutiérrez explaining that an end to NAFTA would hurt Mexico a lot but that it's "also going to hurt the United States." It's also part political, with the diplomat saying he's "optimistic about what we've heard from Mr. Lopez Obrador and his transition team."

AMLO, for all his past skepticism of NAFTA, has taken a more conventional approach of late.

That transition has fostered a "general sense of optimism" about trade in the business community, both in Mexico and in the U.S., said Antonio Garza, a former U.S. ambassador to Mexico.

"The positions the president-elect and his team have announced have all been very constructive," said Garza, now counsel at White & Case in Mexico City. "It suggests a commitment and desire for seamlessness in terms of the general direction the current administration has taken on trade."